The present invention refers to a method for initial adjustment of the peripheral register of engraved cylinders of successive printing units of a rotary multicolor printing press in accordance with a determined job. These cylinders are connected to a common drive shaft by respective clutches, according to which an angular register mark is arranged on each cylinder and aligned with a fixed point with respect to the engraved pattern on the cylinder. These angular positions are measured and stored with respect to a zero reference. The invention also refers to a device for performing this method.
For color printing by a plurality of engraved cylinders, the various cylinders must be arranged in angular positions which are accurately determined with respect to one another. The position depends on the length of the web between the various printing units and on the size of the engraved cylinders, i.e. their peripheral or circumferential length. When considering the zero reference of the printing of each engraved cylinder, its position must be determined with respect to the zero position of the other engraved cylinders, according to the length of the web separating two successive printing units and to the peripheral length of the engraved cylinders, so that the successive printings of the different colors on the printed web are in perfect register.
An adjustment device for the register of respective positions of various engraved cylinders of such a press has already been proposed in DE 44 41 246, wherein two segments of the drive shaft between two engraved cylinders are connected by a coupling provided with an endless screw adjusting mechanism for modifying the respective angular positions of two drive shaft segments and consequently those of the two engraved cylinders connected to these respective segments.
Also, U.S. Pat. No. 3,963,902 has proposed a method and a device for repositioning printing cylinders of a rotary multicolor press driven by a common transmission line, into angular register positions known for a kind of job which is periodically repeated. Once the initial adjustment of the printing press is realized by known conventional techniques, i.e. manual adjustment by visually controlling the register of the colors on the printed paper or cardboard web, the respective positions of the different cylinders are determined by means of an angular indexing device and are stored. When the same job is to be run, the cylinders are repositioned in an angular reference position. Then, each cylinder is brought into an angular indexing position by means of a differential device driven by a motor running until the angular position of the cylinder is in register with the indexed position. This operation is repeated for each cylinder. This adjustment can be realized without a printing web positioned in the machine, thus avoiding loss of paper or cardboard.
However, this method requires a conventional initial adjustment for each new job. This adjustment is very time-consuming and uses a large amount of paper or cardboard web. Moreover, resumption of a job involves the semi-automatic positioning by the operator requiring a certain adjustment time on the machine.
A method similar to the preceding one, but using clutches between each engraved cylinder and the transmission line, is described in DE 27 53 433.
Another adjustment method using marks on engraved cylinders and couplings between the cylinders and a transmission line and which are uncoupled from their drives in correspondence with the position of their marks with respect to the marks on the chase for the adjustment of their initial positions is described in EP 0 070 565. This method requires the use of the printing web and thus causes a considerable loss of material for realizing the adjustment. Besides, such a method does not resolve the question of the initial adjustment for a first job on the printing press.